1. Field of the Invention
This invention relates in general to traction and hydraulic elevator systems with distributed control circuits, and more particularly, to a method and control system for protecting against control signal and communication failures with diminished elevator service because of the loss of a vital element in the system.
2. Description of the Prior Art
Computers have heretofore been pre-programmed to perform various functions in the operational control or management of car and hall call response strategies in an elevator system. Various arrangements for elevator bank configurations have been known to benefit from these state-of-the-art solid-state controllers, but assuming that dynamically defined tasks involve uniquely reconfigured failure mode arrangements; these have yet to emerge. Disturbingly present is the likelihood that the failure of components assigned for dedicated control functions, such as in a fixed dispatcher controller used with the present day elevator control apparatus, will eventually interrupt or discontinue to communicate with other controllers in the system. These systems may have a back-up mode of operation with some form of service being retained, but it is of significantly inferior quality to the normal service.
With the introduction of microprocessor based elevator controllers, and the distribution of electronic circuits located with each car and proximate to the respective floors, communication with the remote controllers is of fundamental concern since the integrity of hall call signals and the control strategy in assigning cars to answer these calls is critical to operational efficiency and to the satisfied customer and prospective passengers.
One of the principal problems with a distributed control system for controlling a plurality of elevator cars is that normally the remote controller which has been selected for implementing the control strategy is also responsible for checking the integrity of the communication with the other controllers in the system. In a failure mode the other controllers are not immediately informed and they don't assume the self-selection necessary to begin implementing a master control strategy remaining available to them such as if there were good signal integrity between this controller and the hallway serial link of corridor communication.
Another problem is in the situation where there is a failure of the master controller and all of the remaining controllers simultaneously begin to assume the task of dispatcher for the bank of cars because there is no priority of command for controllers and there is insufficient communication to alert each controller as to the redundancy of controllers in the system. Asserting the authority of master controller by each would result in the potential for multiple car assignments to the same floor and inexcusably not the best car efficiency for the bank of cars which still has the potential for providing efficient service and to minimize waiting time.